The present invention relates to data storage systems, and more particularly, this invention relates to optimally positioning an idle robotic accessor in a tape library to minimize access time.
Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is typically stored on media of data storage cartridges that are, in turn, stored at storage slots or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such data storage cartridges are commonly termed “removable media.” Data storage cartridge media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, CompactFlash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically comprise data storage drives that store data to, and/or retrieve data from, the data storage cartridge media. Further, automated data storage libraries typically comprise I/O stations at which data storage cartridges are supplied or added to, or removed from, the library. The transport of data storage cartridges between data storage slots, data storage drives, and I/O stations is typically accomplished by one or more accessors. Such accessors have grippers for physically retrieving the selected data storage cartridges from the storage slots within the automated data storage library and transporting such cartridges to the data storage drives by moving, for example, in the X and Y directions.
In an effort to increase storage capacity, deep slot technology allows for storage cells that contain more than a single data storage cartridge. Such storage libraries allow for higher density, or more cartridges stored per square foot. In ‘deep slot’ libraries, two or more cartridges may be stored in a multi-cartridge deep slot cell, arrayed in series, one behind the other, in tiers ranging from a frontmost tier to a rearmost tier.
In the near future, with the adoption of improved media, the cost of storing information (on a per byte basis) on tape is expected to decline by a factor of five or more with respect to magnetic disk. Also, short-term and long-term reliability will continue to favor tape-based storage. Furthermore, as more mass storage is allocated to cloud networks, most storage will be in large libraries, rather than on individual drives, which is a consideration favoring tape-based storage. One historical disadvantage of tape-based storage with respect to disk-based storage was the relatively poor access time associated with tape-based storage, with the time required to bring the tape to the tape drive and then spool the tape to the file location typically averaging about 40 seconds in some systems.